1. Field of the Invention
The present invention relates to a vacuum regulating valve for regulating the pressure in an evacuated vacuum vessel for chemical reaction included in a physical or chemical machine or the like.
2. Description of the Related Art
A chemical process, such as an etching process, is carried out in a vacuum vessel included in a semiconductor device fabricating system. The vacuum vessel is evacuated at a negative pressure by a vacuum pump. A pressure regulating valve is placed in an external line connecting the vacuum vessel to the vacuum pump. A pressure regulating valve disclosed in JP-A No. 8-178126 has two ports connected, respectively, to a vacuum vessel and a vacuum pump, internal passage connecting the two ports, a valve seat formed in the internal passage, a valve element to be seated on the valve seat to close the pressure regulating valve, and a piston for operating the valve element. The stroke of the piston corresponds to a full valve opening of the pressure regulating valve.
Different vacuum vessels have different volumes and different vacuum pumps have different evacuating capacities, respectively. Therefore, it is desired to adjust the valve opening of the pressure regulating valve according to related conditions. Since the degree of vacuum in the vacuum vessel varies according to the rate of supply of reaction gases, a pressure change in the vacuum vessel must be compensated to maintain the interior of the vacuum vessel at a desired negative pressure. If the pressure regulating valve is always fully open and the valve opening is not regulated, discharge rate at which gases are discharged from the vacuum vessel cannot be regulated and, consequently, the pressure change cannot be accurately compensated.